\section{Introduction}

The Earth's atmosphere presents a number of problems to astronomers wishing to make precise, high resolution astronomical observations at ultra-violet, visible and infra-red light wavelengths. The constant movement of different layers of the atmosphere results in rapid changes of refractive index, causing a blurring that can be difficult to compensate for, even with recent advances in non-linear deconvolution techniques. Moreover, certain wavelengths of interest are strongly attenuated by the atmosphere, and naturally occurring weather conditions can prevent any observations being made at all. 

Astronomers have long been aware of the negative effects of the Earth's atmosphere on their observations. Great engineering efforts have been made to locate telescopes in places which have favourable viewing conditions, but which are usually very inhospitable as a result, such as the recently announced \textdollar1.3bn Extremely Large Telescope on a mountain in the Chilean Desert, which has the lowest known abundance of life on the planet \cite{atacama}.

Moreover, observational instruments have been put into orbit to escape the atmosphere altogether, at great expense and imposing enormous engineering constraints upon the instrument. Observation platforms such as \emph{Hubble} have particularly benefited from the greatly reduced attenuation of near-infrared wavelengths, which the water in the atmosphere so strongly absorbs.

The advantages of observations from above the atmosphere are clear, but the cost of putting telescopes into orbit is exceptionally prohibitive. Scientific high altitude balloons have been in development since the end of the second world war, and advances in polymer research and production techniques now make it possible for scientific payloads to be routinely lofted to altitudes of 35km above sea level. Most international space agencies have a division devoted to scientific ballooning, and organisations such as NASA's Columbia Scientific Balloon Facility launch balloon envelopes of up to 1.12 million m$^3$ volume, which can loft payloads of three tonnes to 40km altitude for several weeks \cite{csbf}.

The Cambridge University Spaceflight group \cite{cusf}, of which the author is a member, routinely launches latex weather balloons to altitudes of up to 35km. These balloons can loft payloads of several kilograms to this altitude, and the group has been involved in the development of recent valve and ballast techniques to cause the balloons to maintain a specific altitude. At the altitude at which the photograph in Figure \ref{fig:estimation_nova8earth} was taken, the atmospheric density is \textless 1\% that of sea level pressure, and attenuation in the infra-red is minimal. 



\begin{figure}[!htbp]
  \centering
  \includegraphics[width=\textwidth]{estimation/rawpics/nova8earth.jpeg}
  \caption{A photograph taken from a Cambridge University Spaceflight balloon from an altitude of 32km}
  \label{fig:estimation_nova8earth}
\end{figure}

The goal of this project, therefore, is to investigate the feasibility of designing and building a small stabilised high altitude platform (as a proof of concept) for astronomical observations, to be lofted by a latex weather balloon, making use of recent advances in the development of low cost, commercially available embedded sensors and computers. 
